When a skill book is used, you gain one skill point.
List of known skill books: 
- Farglow, Goblin Training Area, On top of one of the big rocks.
- Broken Valley, Village, Black Boar Inn, 3rd floor locked door (lockpicking 2 required), strange tome, three parts.
- Broken Valley, Secret Passage, Secret room with pressure plate, behind big spiderweb. Inside a chest (lockpick 2 required).
- Broken Valley, Citadel Dungeon, Into Thin Air. Activate the pedestals, then the switch to initiate a cut scene where a variety of weapons on chains come down from the ceiling. The skill book is on a chain that is hidden in a corner near Romon's corpse. Warning, once you pick up an item on a chain, all other items will retract to the ceiling where they are unobtainable!
- Broken Valley, Naberius Storage. Must mindread Naberius for the password to the door. Must get 4 Parchments and show them to Zixzax to get password for the teleporter to get to the door.
After Battle Tower:
- DKS - Completing each your platform operators' quests results in a skill book being awarded for each request.
- Orobas Fjords, Sinister Cavern, Book in the chest near the Book of the Dead.
- Orobas Fjords, High Hall Mines, Near where Mundus is located.
- Orobas Fjords, Red Hammer Tribe's Cave, Book on the bench behind the only door.
- Kali's Flying Fortress Headquarters, After killing Kali read The Demon Wars for 3 extra skill points.
- Stone's Flying Fortress Greenery, Drop black rose and moonshine into the spring for 1 extra skill point.
- Ygerna's Memory, at the very end of game, behind you where you start.
Flames of Vengeance
You'll get a skill book as part of a reward in just about any side quest.